We developed quantitative models of the cell-to-cell communications via cytokines amongst population of T lymphocytes. Our goal is to understand how T cells self-organize to decide their cell fate (e.g. between quiescence -tolerance- and death/proliferation -responses). At a fundamental level, we developed theoretical tools to analyze the heterogeneity and synchronicity of T cell responses in dense tissues. In the context of responses to tumor, we found that a critical mass of T cells existed to drive tumor rejection. Additional work is being carried out to dissect quantitatively how T cell decide collectively between tumor rejection and tumor tolerance.